1. Field of the Invention
The present invention relates generally to a zoom finder, and more particularly to a zoom finder which is able to prevent an image from shifting.
2. Description of Related Art
A conventional zoom finder has a finder optical system which is composed of an objective lens including two movable lenses, an erecting optical system, an eyepiece, etc. One end of both movable lenses is supported movably along the optical axis by a guide shaft, and the opposite end of both movable lenses engages with a rotation preventive member. The movable lenses are pressed by a spring so that cam followers provided at the movable lenses can be in contact with cam faces of a finder cam. Thus, by driving the finder cam, the two movable lenses are moved along the optical axis in a certain relation to thereby change a magnification of the zoom finder.
When the two movable lenses are moved by driving the finder cam, a frictional force is produced between the cam face of the finder cam and the cam follower of the movable lens. The frictional force acts on the cam follower so as to rotate the movable lens around the guide shaft. Although one end of the movable lens engages with the rotation preventive member, the movable lens is rotated a little by the frictional force since there is some play between them. When the driving directions of the finder cam are switched, the directions of the frictional force are also switched, and then the rotational directions of the movable lens are switched. Thus, the conventional zoom finder has a problem in that the image observed through the finder shifts whenever the driving directions of the finder cam are switched, as a result of the shifts of the movable lenses.